In my opinion, Exodia is the least overpowered because it's practically impossible to draw all pieces in one game (unless you're running that cheap exodia deck lawl). Judgement Dragon has a reasonable summoning condition and its effect is amazing, but not broken. I've never seen the cards Makra and Exchange because no one uses them so those don't matter all that much. Which leaves BLS and Brionac. BLS is so broken compared to Chaos Sorcerer because it has more attack, an extra broken effect of attacking twice, and they both have the same summoning conditions so therefore it's overpowered. Brionac though is the most overpowered because it can just send cards back to the hand and attack directly every turn which is too good for a level 6 synchro monster.

maybe a little wait but i think a card thats not even up there is most OP ever heard of Dancing Fairy? if you have a few good counter traps on your field you cn quickly double or even triple your lifepoints.